The present invention is an improved version of the lamp switching device described in U.S. Pat. No. 4,700,110, "Lamp Switching" and a related patent application, entitled "Electromechanical Lamp Switching." (PLEASE INSERT APPLICATION NO.)
The invention is intended for use in an electrical lighting circuit wherein two or more lamps are connected in common to a single wall switch and it is desired to control the level of lighting by selectively switching a subset of total number of lights upon alternate operations of the wall switch. In such a system, the lighting units may typically be fluorescent fixtures with two ballast circuits each supplying one or more lamps. A switching device according to this invention may be installed in some or all of the lighting units, or may control a set of lighting units by means of an ordinary relay.
Initially, each switching device is preset with power applied to switch on the lamps controlled thereby, so that all of the lamps controlled by the wall switch are on. Thereafter, each successive application of power by means of the wall switch causes the controlled lamps to alternate between off and on states, resulting in dim or normal lighting.
Such switching devices, as described in this application and the patent and pending applications previously referred to, ensure a strict alternation between on and off states for each switching unit, ensuring that multiple units will remain in step with each other and that no matter how long the period between new applications of power to the lighting circuit, the memory of the preceding state will be retained. This non-volatile memory of the preceding state may be embodied in a number of physical device types, the preferred embodiments disclosed in the referenced patent and in this application using a magnetic latching relay, which combines the memory and switching functions in one component.
Whereas the previous invention has advantages in requiring very low operating power and therefore being applicable to energy-saving lighting fixtures, the circuits described previously in the referenced patent required high-voltage components as they were designed to work directly from the typical a.c. line voltage of 117V.
The present invention is a further refinement which enables the circuitry to operate at a much lower regulated voltage derived from the a.c. line voltage through power conditioning means, while still consuming very low operating power. This has advantages in reducing the cost of components and improving the reliability, since the high voltages coupled with high operating ambient temperatures can cause gradual degradation of the devices used in the previous invention.